learn only 3 things about them ...
Feather stars are rarely found near the shore.
Most species can move about from place to place.
long spiny arms are fragile and break easily. Don't disturb
seen? These feathery animals are sometimes seen on some
of our shores, generally near living reefs. They are also encountered
by divers on our Southern reefs.
What are feather stars? Feather
stars belong to Phylum Echinodermata.
Although they may look similar to brittle stars, feather stars belong
to a different Class Crinoidea. 'Crinoidea' means 'lily-like' in Greek.
There are about 600 known living species of feather stars. Shallow-water
crinoids are also called comatulids.
Features: Like other echinoderms,
feather stars are symmetrical along five axes, have spiny skin and
tube feet. Like brittle stars, feather stars have thin, long and highly
flexible arms. But crinoids are much more spectacular than brittle
stars, with an explosion of long feathery arms.
The arms arise from a cup-shaped structure at the centre called the
calyx. The calyx contains the digestive system and is covered by a
soft membrane called the tegmen that may be rounded into a mound or
look like a drum skin over the calyx. Unlike sea stars and brittle
stars, the feather star's mouth facing upwards. The mouth may be in
the centre of the disk or off to one side. The anus is also on the
upperside, in some species at the top of a cone or tube that brings
it above the feeding current to prevent fouling of the feeding process.
The side of the feather star that faces downwards has a claw-like
appendage called the cirri that is used to grip the surface.
Sometimes confused with brittle
stars which also have bristley arms. But brittle stars usually
only have 5 or 6 arms. More on how to tell apart bristley
animals and feathery animals.
An armful: Juvenile feather stars
start with 5 arms but repeatedly grow back two arms in place of each
arm branch that is shed. This branching happens near the calyx. Thus
feather stars usually have arms in multiples of 5, most have at least
10 arms. Some can have 80-200 arms!
The arms are made up of large, well developed, jointed ossicles (plates
made mostly of calcium carbonate). The ossicles are connected together
like a bicycle chain. Along the length of the arms are rows of tiny
finger-like structures called pinnules that give the animal its feathery
look. Each pinnule is jointed and has a groove down the middle that
joins to a groove running down the length of the arm. The grooves
are lined by tube feet that produce mucus. Unlike in sea stars, the
tube feet do not play a part in moving the animal but are used in
collecting food and to breathe. The pinnules near the mouth protect
the mouth from harm and keep the area clean.
What do they eat? Feather stars
feed on tiny drifting organisms and particles, gathering these passively
from the water by adjusting their arms to maximise the filter feeding
area relative to the water flow. The arms may form a flat fan or may
be curved into a parabola like a satellite dish. Some may hide in
crevices and only stick out some part of their arms to gather food.
The mucus covered arms have tiny tube feet that flick edible bits
into the grooves of the pinnule and arm. These bits are then slowly
transported along the groove to the mouth.
Shy stars: Most feather stars
only come out to feed at night. During the day, they hide in crevices
or among coral, curling up their arms in tight coils.
Swimming stars: Feather stars
can move about by moving their arms. They crawl over soft sediments,
using their arms to drag themselves over the surface, lifting up the
central portion of their bodies. Their arms and pinnules have tiny
hooks that catch on the surface. They can also swim by thrashing their
arms in the water in co-ordinated strokes. However, feather stars
usually only crawl or swim to get away from predators. They usually
don't move around very much once they find a good spot to settle on.
Feather stars are usually perched on top of tall living or dead hard
corals, sponges and other sturdy anchors. Here, they extend their
arms into the currents and gather food.
Falling apart: Like
brittle stars, feather stars can purposely drop off an arm or two
when threatened. The dropped arm may continue to wriggle to distract
the predator while the brittle star escapes. The feather star is able
to do this because the ossicles in its arms are connected by mutable
connective tissue. The feather star can rapidly change the consistency
of this tissue from rock hard to almost liquid. The arm eventually
re-grows, but it takes about a month before it is fully restored.
Fishes are the main predators of feather stars.
Old stars: Feather stars are the most ancient and considered
the most primitive of echinoderms. In the fossil records, there were
10 times more feather stars and sea lilies than there are today.
Star on a stick: Stalked stars,
called sea lilies, are mostly found in deep waters 100m or lower.
There are about 80 species of sea lilies. Some living sea lilies can
have stalks up to 1m long!
Feather star babies: Feather stars
have separate genders and are usually either male or female. The eggs
and sperm are produced in swollen pinnules near the base of the arms.
These are released into the water for external fertilisation. Feather
stars undergo metamorphosis and their larvae look nothing like the
adults. The form that first hatches from the eggs are bilaterally
symmetrical and free-swimming, drifting with the plankton. They eventually
settle down and develop into tiny stalked feather stars. After a few
weeks, the cirri form and the little feather star breaks free from
the stalk to become a free-moving adult.
Living off a star: Various small
crabs, shrimps, worms, brittle star and other tiny animals may live on a feather
star. Some are found no where else.
Human uses: Feather stars are
not widely used for human purposes. Although they almost invariably
die a slow death from starvation in marine aquariums, they are sometimes
taken for the live aquarium trade.
Status and threats: Some of our
feather stars are listed among the threatened animals of Singapore.
Stephanometra spicata, described in the 1960's as one of the
most common feather stars on our shores, is today listed among the
threatened animals of Singapore. Lamprometra palmata and
Stephanometra indica were considered common in the late 1990's
but were rarely encountered in a survey of echinoderms in the early
2000's. Like other creatures of the intertidal zone, feather stars
are affected by human activities such as reclamation and pollution.
Trampling by careless visitors also have an impact on local populations.
Clinging on with the cirri.
Beting Bronok, May 06
Some can be tiny.
Tanah Merah, Oct 09
Beautiful shades and colours.
Changi, Jun 08
tube feet on the pinnules.
Pulau Hantu, Jan 12
Channels along the pinnules and arm.
Sisters Island, Aug 12
Pink eggs in the pinnules?
Sisters Island, Aug 12
Regenerating arm tips.
Chek Jawa, May 05
St John's Island,
Photo shared by Marcus Ng on flickr.
Sisters Island, Aug 12
Sisters Island, Feb 15
Photo shared by James Koh on flickr
stars on Singapore shores
Crinoidea recorded for Singapore
*from C. G. Messing & T. S. Tay. 29 June 2016. Extant Crinoidea (Echinodermata) of Singapore
in red are those listed among the threatened
animals of Singapore from Davison, G.W. H. and P. K. L. Ng
and Ho Hua Chew, 2008. The Singapore Red Data Book: Threatened
plants and animals of Singapore.
seen awaiting identification
Feather star species are difficult to positively identify without
dissection and examination of internal parts. On
this website, they are grouped by external features for convenience
Capillaster cf. tenuicirrus
Comatula cf. solaris
Comatula cf. pectinata
||Amphimetra cf. discoidea
Heterometra cf. crenulata
Himerometra robustipinna (Red feather star) (DD: Data deficient)
indica (VU: Vulnerable)
- C. G. Messing & T. S. Tay. 29 June 2016. Extant Crinoidea (Echinodermata) of Singapore. The Raffles Bulletin of Zoology 2016 Supplement No. 34 (Part I of II) Pp. 627-658.
- T. S. Tay & J. K. Y. Low. 29 June 2016. Crinoid diversity in the subtidal non-coral reef habitats of Singapore. The Raffles Bulletin of Zoology 2016 Supplement No. 34 (Part I of II) Pp. 659-665.
- Charles Messing. 16 October 2015. New record of the featherstar Cenometra bella in Singapore. Singapore Biodiversity Records 2015: 160
- C. G. Messing & T. S. Tay. 29 June 2016. Extant Crinoidea (Echinodermata) of Singapore. [pdf] The Raffles Bulletin of Zoology 2016 Supplement No. 34 (Part II of II) Pp. 627-658.
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